Press for dental investment material



Dec. 16, 1958 w. D. KELLEY PRESS FOR DENTAL INVESTMENT MATERIAL 2Sheets-Sheet 1 Filed July 8. 1954 INVENTOR l l fl/l'anv 0. Kelley HISAGENT Dec. 16, 1958 w. D. KELLEY PRESS FOR DENTAL INVESTMENT MATERIAL 2Sheets-Sheet 2 Filed July 8. 1954 I J m y Mk N 9 1 E 0 35%; m \\\x H. WMM w Uf HIS AGENT United States Patent 2,864,125 PRESS FOR DENTALINVESTMENT MATERIAL William D. .Kelley, Dallas, Tex. Applicati0nJuly8, 1954, Serial No. 442,155

2 Claims. (Cl. 185.7)

This invention relatesto improvements in presses and more particularlyto presses used in connection with investment molding material used incasting small metallic parts, such as dental inlays and thelike.

While the present invention is particularly adaptable for use bythedental profession, in casting inlays and the like, it is tobe understoodthat it is equally adaptable for use inconnectionwith the casting ofjewelry and other small metal parts, which are usually cast underpressure, as in ,a, centrifugal casting machine or the like.

The present inventionis so designed as to provide a press whereby thedensity of the plastic material, such as dental investment material,plaster of Paris, and the like, maybe subjected to pressure immediatelyafter the initial mixing and such pressure will be maintained on thematerial until it has completely set, which relieves the material ofporosity due to air bubbles, which deter fromthe molding of a smoothfinished metallic piece, such as an inlay.

An object of this invention is to provide a dental press, whereinpressure may be applied to investment material so as to relieve theinvestment material of voids and air bubbles so as tomake the moldingmaterial more dense.

Another object of the invention is to provide a mechanically operated,hydraulically responsive dental press that may be easily manipulated byhand, yet one which will give an accurate indication of the exact amountof pressure being applied to the investment material.

Still another object of the invention is to provide a press for dentalinvestment material that may be readily assembled and disassembled forthe removal of the investment flask to enable the molding of the inlayor the like.

A further object of the invention is to provide a screw actuated,hydraulically responsive dental press that is self-contained. i

A still further object of'the invention is to provide a manuallyoperated, hydraulically actuated press element wherein the hydraulicpump and motor are contained within a single cylinder.

Yet another object of the invention is to provide O-ring sealingelements around the plunger, which plunger extends into contactrelationwith the plastic material being pressed, which sealing elementsprevent passage of plastic material between the plunger and thecylinder.

Still another object of the invention is to provide a dental presswherein the pressure may be applied to freshly mixed plasticinvestment'material with the correct or an excess amount of watertherein, so when pressure is applied the excess water may be pressed outof the investment material. thereby automatically giving an investmentmaterial the correct setting expansion.

With the foregoing objects in mind and others that will manifestthemselves as the description proceeds, reference is to behad to theaccompanying drawings, in which like reference characters designate likeparts in the several views thereof, in which:

Fig. l is a perspective view of the manually operated,

2,864,125 Patented Dec. 1.6,

2 hydraulically responsive press taken from the top and a side thereof;v Fig. 2 is a vertical sectional view taken through the device, asshown-in Fig. 1, with parts broken awayv and shown in elevation to showthe details of construction;

Fig. 3 is a sectional view taken on the line 33f of Fig. 2, looking inthe direction indicated by the arrows; Fig. 4 is a cross-sectional viewsimilar to that shown inFig. 3, but taken'on the line 4--4 of' Fig. 2,looking in the direction indicated by the arrows;

Fig. 5 is an elevational view of a modified formof invention, with partsbroken away and shown in section to bring out the details ofconstruction; i Fig. 6 is a sectional viewtaken on the line 66-of Fig.5, looking in the direction indicated by the arrows; and t Fig. 7 is afragmentary vertical sectional view with parts broken away and shown insection, of the .upper portion of a modified formof the invention, thelower part being substantially as shown in the form of. the inventionillustrated in Fig. 2.

First form of 'invention With more detailed reference to the drawing,asehpwn in Figs. 1 through 4, the numeral. 11. designates a tubular basewhich. is. internally threaded at the. respective upper and lower ends,as indicated'at 12 and 1,4, as is bes t seen in Fig. 2. The hydraulicassembly -unit, generally designated by thenumeral 16, has externalscrew threads :1 the lower. end, which are adapted to interfitgwithscrew threads 14. A plate 20 is secured to the lowe r end of thehydraulic member 16 by means of screws 22 and has a spring 2 interposedbetween theplate ZO-and the lower face of a shouldered piston 26, whichis fitted within cylinder 28. A sealing element, such as a rubber cupmember 30, is fitted above shouldered piston 2 6Qso as to form a fluidtight seal with the cylinder 28. to prevent leakage of hydraulicfluidoutward thereby. The lower end of shouldered piston, 26 has a plunger 32thereon which is adapted to extend through an aperture formed withinpartition plate 34, when the plunger is in extended position. Theplunger has annular grooves formed therearound, which are preferablysquare in cross section, and which annular grooves receive Ov-rings 3 6.

A molding flask, which comprises an upper rubber portion 38 which has ahole 40 formed thereth rough, which hole is tapered at the upper endthereof, but which is'in tight fitting relation with the plunger 32 forthe greater part of its length, which enables the plunger 32 to form atight seal within the hole 4t! while the press is being used. The rubberportion 38 has an annular groove around the under side thereof tocomplementarily receive the upper end of cylindrical ring 42, the innerportion of which form the mold cavity. The lower end, rubber cap portion44 forms a seal for the lower end of the ring 42, which cap portion hasan upwardly extending conical portion 46 which serves to form a funnelor neck to provide for the introduction of material into the mold cavitywhen an inlay or the like is being molded. A pin 48 is centrally mountedwithin the upwardly extending neck portion 46 and is adapted to receivea wax model on the upper end thereof, which wax model is designated at50. 'When plastic material is poured into the m old cavity formed in thering 42, the plastic investment material will surround the wax model.However, under normal conditions, the investment material will be ladenwith minute to large air bubbles, but, with a molding flask comprisingthe upper rubber portion 38, the ring portion 42, and the lower capportion 44, the flask may be placed in the lower end of the tubular basemember 11 so it will abut with the partition 3.4. With the device inthis position, a screw-threaded plug 52 is screwed into screw threads 12until the flask is in secure relation with respect to the tubular base.It is preferable to have the plunger 32 arranged so that it will extendsubstantially flush with the lower end of plug 38 when in pressing positon, so as to present the investment block with a substantially smoothupper end. With the device arranged in this manner, it is ready toinvest a model of a dental inlay or the like.

The upper portion of the cylinder 28 has cupped piston member 54, whichpiston is attached to a screw-threaded bolt 56 by means of a hollow bolt58, which hollow bolt 58 interconnects with a passage 60 withinscrew-threaded bolt 56. The bolt 56 threadably engages a shoulderedportion 62 of the piston 54, so upon rotation of the head of bolt 64,the piston 54 is forced downward. It is preferable to have the headportion 64 of the bolt knurled or otherwise roughened or irregular inshape, so as to enable the gripping thereof by hand. It is alsopreferable to have the cylindrical portion designated at 16 adjacent thehead portion 64 roughened or knurled so as to enable it also to begripped by hand, to enable the operation of the bolt 56.

A pressure gauge 66 threadably engages the upper end of bolt 56 andconnects with passage 60 so that the pressure of fluid entrapped betweenpiston cups 30 and 54 may be read on the gauge 66.

A dowel pin 68 interconnects bolt 56 and piston 54 to prevent relativerotation therebetween to prevent rotation of the head 64.

Operation of first form of invention The flask F, which comprises theupper rubber portion 38, the cylindrical ring 42, and the lower capportion 44, is inserted within tubular base member 11 and with the waxmodel 50 in place on the sprue pin 48, investment material is pouredthrough opening 40 until the cavity within the ring 42 is filled withthe material extending up into hole 40, and with the plunger 32 inretracted position, the cylinder portion 16 is screwed into place in theupper portion of tubular base member 11 and without any pressure withincylinder 28, the spring 24 will hold the piston 26 in raised position,and the screw threaded bolt 56 will be in upward position with thepiston 54 a spaced distance from piston 30, and with the chamber betweenthe pistons 30 and 54 filled with suitable fluid, such as hydraulicfluid, the head 64 is rotated so as to screw bolt 56 downward to urgepiston cup 54 toward the piston cup 30. The pressure will cause thepiston 26 to move downward to compress spring 24 to urge plunger 32downward into hole 40, which is in tight fitting relation with respectto the plunger and with plastic investment material extending into theopening 40, the pressure of the screw bolt member 56 will be transmittedthrough hydraulic fluid to cupped piston member 30 which will urge theplunger 32 downward into contact relation with the plastic material,which is made chiefly of a chalky solid and water, such as plaster ofParis, dental investment stone and the like. As the pressure isincreased on the plastic material within the cavity of the flask F, theair bubbles within the material will be compressed until they arepractically non-existant, and the voids made thereby will be filled withsolid material. The pressure can be minutely controlled and gauged bythe pressure gauge 66 so that the wax model 50 will not be damaged. Theflask containing the plastic material may be left under pressure untilthe material is completely set. In this manner a dense block ofinvestment material may be formed with the wax model therein, so uponremoval of the investment block from the press, the rubber portion 38and cap portion 44 may be removed from the cylinder ring 42, and afterremoving the rubber portion 38 and the lower cap portion 44, thecylindrical ring may be reinserted within the lower portion of thetubular base 11,

so the lower edge thereof will rest on the upper face of screw-threadedplug 52, then upon applying pressure again to the plunger 32 and to theupper end of the investment block, the investment block will be moveddownward along the inner taper of the cylindrical ring 42 a sufficientdistance to loosen the block from the cylindrical ring which will permitready removal thereof and with the investment block now being removedfrom the forming flask, it may be heated in the usual manner, to removethe wax, and placed in a pressure molding machine for molding the inlayin the usual manner.

An alternate method of introducing plastic material into the cylindricalflask F, is to assemble the parts together with the wax model 50, of theobject to be cast, in place on sprue pin 48, then plastic investmentmaterial is poured into opening 40 until the investment material issubstantially level with the top of the rubber portion 38, and while thematerial is still plastic, the entire flask assembly, comprising therubber portion 38, cylindrical ring 42 and cap portion 44, is insertedthrough the open end of tubular base member 11, then the screw threadedthumb nut 52 is screw threaded into the lower end of tubular base member11 until it is in binding engagement with the lower end of the flask,whereupon, hydraulic fluid pressure is ready to be applied in the mannerhereinbefore set out.

Second form of invention The form of invention, as disclosed in Figs. 5and 6, shows a device, the operating mechanism of which, including thetubular base 11, is substantially the same as the form of the inventionillustrated in Figs. 1 through 4, and described above. However, thisform of the invention utilizes a base 71 in which a rubber bottom cap 72is fitted, which cap has an annular groove 74 formed therein, whichgroove is spaced radiallyinward from the outer periphery of the cap toreceive the lower end of a cylindrical ring member 76. A cap portion 78has a screw threaded neck portion 80 thereon which threadably engagesscrew threads 12 that are formed within the cylindrical base portion 11.A rubber cap portion 79, having a hole 81 formed therein, is fittedwithin the cap portion 78. The inner cylindrical bore of the neckportion 80 has fitted therein an enlarged piston element 82, with O-ringelements 84 thereon, to form a sealing engagement between the piston andthe bore of the neck. The upper end of the piston 82 has a connectingrod 86 thereon, the upper end of which is reduced and threaded, asindicated at 88, to threadably engage a threaded hole 31 in the lowerend of plunger 32. By removing a blind screw 33 from the lower end ofplunger 32, the connecting rod 86 may be connected thereto, so the flaskmember, designated at 90, and comprising a base plate 71, bottom cap 72,cylindrical ring 76, cap portion 78, and upper rubber cap portion 79,may be connected thereto. The flask is held together by means of posts92 which threadably engage the base 71 and extend upward. The upper endsof the respective posts 92 are reduced, as indicated at 94, to telescopeinto the respective holes 96 formed in the upper cap 78. A thumb screw98 passes through the respective holes within cap plate 78 andthreadably engage ascrew-threaded hole which is formed within therespective ends of the posts 92.

The respective lower and upper caps 72 and 79 have annular grooves 100and 102 respectively formed therein, which are spaced radially inwardfrom the outer periphery thereof to receive the respective lower andupper ends of cylindrical ring member 76. The hole 81 is in registerwith the cylindrical bore formed in upstanding threaded neck 80 so thatthe piston 92 will travel free from the neck into the cap portion 79, sowhen the cylindrical cup piston 30 is in its lower-most position, thelower end of the piston 82 will be flush with the lower edge of the capportion 79. In this manner a lar e m d web s ndicated at 50a, may bemounted on the sprite pin 4811, than could be mounted in the type offlask shown at F, in the form. of invention described above.

Operation of second form' of invention When it is desired to mold alarger object than may be received within the flask F, of the form ofinvention as shown in Figs. 1 through 4, the screw 33 maybe removed fromthe end of the plunger 32 and the upstanding connecting rod 86screw-threaded into the lower end of the plunger 32, then, with theflask 90 clamped together by thumb screws 98, and with the model 50a inplace on sprue pin 48a, and with the flask 90' separated from thetubular member 11, plastic investment material is introduced into flask90 until the screw threaded neck portion 80 is substantially filled.Whereupon, the neck portion 80 is screw threaded into the lower end oftubular base memberll so that the piston 82 will register with thecylindrical bore of neck 80', whereupon the method of applying pressureto the plastic material isthe same as set out for the form of theinvention as illustrated in Figs. 1 through 4, and described above.

After the piston 82 has applied pressure to the plastic material tocompress the air bubbles therefrom, so as to render the investment blockmore dense, a predetermined amount of pressure is maintained thereonuntil the plastic investment material is thoroughly set, whereupon, thethumb screw 98 is loosened to enable the removal of the flask 99 frombetween the base plate 71 and the upper cap portion 78, then by removingthe upper and lower cap members 72 and 79, the cylindrical. ring 76 maybe reinserted between base plate 71 and upper cap 78, and the thumbscrew 98 tightened, and with the cylindrical member 76 resting on thebase plate member 71, and with the lower face of the investment blockbeing a spaced distance upward from the lower end of the cylindricalring 76, and with the piston 82 either in contact relation with theupper face of investment block within cylindrical ring 76 or resting onproper spacer elements which are interposed between piston 82 and theupper face of the investment block, pressure may be applied to thepiston 82 by the rotation of upper knurled portion 64 of screwthreadedbolt 56, whereupon, the piston 82 will move the investment blockdownward along. the inner tapered surface of the cylindrical ring 76 tobreak the bond therebetween to permit the ready removal of the block.

It is to be pointed out that this arrangement allows differentsizeflasksto be used with. the same pressure generating elements, and ifdesired, the pressure gauge may be arranged to carry dual calibrations,in event the pistons acting upon the plastic investment material havedifferent cross-sectional areas. However, it is to be understood thatwhile piston 82 is shown to be of larger crosssectional area thanplunger 32, it is within the scope of the present invention, to use aplunger of a size to fill the needs of the particular job at hand.

By utilizing a flask or ring, as indicated in Figs. and 6, two or moresmall rings similar to the ring 42 and lower cap portion 44,respectively, with wax models, such as indicated at 50, the cap portionmay be seated on the upper face of the lower cap portion 72, and withthe rings 42 open at the top, the ring 76 and rings 42 may be filledwith plastic investment material so when pressure is applied by plunger82, equal pressure will be applied to investment material within each ofthe rings 42, and since the pressure is equal in all directions on thewax model 50, production molding may be easily performed in this manner.

Third farm of invention The form of the invention, as shown in Fig. 7,has a tubular body member 111 that has the lower portion thereof ofsubstantially the same construction as the tubular base 11, and which isadaptable for use with either form of flask F or 92. The upper portionof the tubular body 111 is screw threaded, as indicated at 112 tothreadably" receive a hollow screw-threads.d" bolt; 1 14, whichhasthreads 116.- The hollowportion of the-bolt isw a cylindrical bore118 that is adapted tolreceive a piston cup 120 therein, which cupis'fitted on theupper end of piston member 122, in substantially thesame manner as the form of the-invention asdescribed above. How, ever,the upper end of the cylindrical bore 118 is closed and a pressure gauge66, which has a threaded connection thereon, threadably engages ascrew-threaded hole 124 which interconnects with cylindrical bore 118;The pressure gauge 66 sealsthe upper end of cylindrical bore 11% influid tight relation. A spring 126 is. interposed between the shoulderedupper endof cylindrical bore 118 and the cylindrical cup member 120, soas to normally urge plunger 132 downward. The-plunger 132 has a threadedhole 131 in the lowenend thereoflwhich normally receives a blind screw133. The plunger-132 is maintained in place by an. annularscrew'threaded ring 134 that is screw threaded into the lower end ofscrewthreaded bolt 114. However, it is in loose fitting relation withthe plunger 132 so as to enable; the relative turning, and the slidingof the plunger 132 with respect to the annular ring 134.

It will be seen that this form of invention eliminates the upper cupmember and the mechanism incident thereto, and it is to be pointed outthat this form of pressure applying arrangement can be used either withthe flask F, asshown in Figs. 1 and 2, or with flask asshown in Figs. 5and 6. The results and operation with respect to the insertion andremoval of the flask is the same as for the aforementioned forms ofinvention.

I Operarionof third form. of invention With the screw threaded bolt 114screwed to the uppermost position, and with the flask F or 90 filled,in" the manner hereinbefore set out, and in place, the knurled head ofbolt 114 is turned to screw the bolt downward into the tubular body 111as the spring compresses, and with the hydraulic fluid withincylindrical bore 118, the plunger 132 is forced downward into opening 40of flask F to apply pressure. to the plastic investment material thereinto compress the air bubbles therefrom, in the manner described for theforms above. In this manner the fluid pressure is applied to thepressure gauge 66 directly through threaded connection 67, when themaximum pressure to be applied is attained, theplastic material may beallowed to remain. in the flask until completely set, whereupon, it isremoved therefrom in the manner set out above.

It is to be pointed out that the form of the invention as shown in Fig.7 may be constructed of fewer parts than the previously described formsof the invention, thereby reducing the cost thereof. By having a singlepiston cup positioned within cylindrical bore 118, the possibility ofleakage of the hydraulic fluid is minimized.

By the use of a relatively thin mixture of investment material, thematerial will flow around the body of the wax model so more minutedetail may be obtained and the possibility of thick material abridginginterstices, which would result in an imperfect casting, is eliminated.

By having the setting expansion of the dental material and thethermo-expansion of the gold equal, a high degree of accuracy isobtained in the casting. By the application of the pressure to theplastic investment material, the air bubbles within this material arereduced to approximately one-ninth their size under forty-five poundspressure.

It is to be further pointed out that the shrinkage of gold isapproximately 2.5% when cooled from the molten state to normaltemperature, and since the accuracy with which dental inlays must bevery exact, it was necessary heretofore to adhere to a very strictwater-powder ratio to give the correct setting expansion of theinvestment material, which is approximately 2.5%, therefore ifthewater-powder ratio varied, the accuracy of the finished casting wasimpaired. However, with the present arrangement, the excess water ispressed out of the mixture until the mixture contains the correct proportions of water-powder to give the correct setting expansion ratio. Inthis manner, it is not necessary to adhere to the exact water-powderratio in mixing the investment material, in fact better results may beobtained by the use of a relatively thin investment mixture, as long assufficient water is added, or any excess, the pressure of the plungerforces the excess water out of the investment ring, giving the correctwater-powder ratio.

While the invention has been described and illustrated in some detail soto the forms shown, it is to be understood that changes may be made inthe minor details of construction, and adaptations made in particularapplications, without departing from the spirit of the invention or thescope of the appended claims.

Having thus described the invention, what is claimed as new and desiredto secure by Letters Patent is:

1. In an investment molding press for applying pressure to plasticdental investment casting material, at least two elongated tubular shellmembers screw threaded together in end to end relation, one of saidshell members having a cylindrical bore formed axially therein, a pairof opposed pistons within said bore, hydraulic fluid between saidpistons, one of said pistons being attached to a hydraulic pressureapplying plunger, which plunger is apertured longitudinally and carriesa pressure gauge thereon which is in communication with said cylindricalbore through said aperture in said plunger, said second piston beingattached to a shouldered, fluid responsive plunger fitted in the otherend of said cylindrical bore, the reduced portion of which plungerextends outward therefrom, a retaining ring surrounding the reducedportion of said shouldered plunger and being secured to the end of saidshell member having a cylindrical bore, a spring interposed between saidretaining ring and said shouldered portion of said last mentionedplunger, said second mentioned elongated, tubular shell member having anabutment intermediate the length thereof, which abutment is centrallyapertured, said reduced end portion of said fluid responsive plungerbeing adapted to extend through said apertured abutment into said lastmentioned tubular shell member, said last named tubular hell memberbeing adapted to receive a molding flask having an axial hole formedtherein, and screw means in said second mentioned tubular member at theend remote from said cylindrical bore, for retaining said molding flaskwithin said tubular member.

2. In an investment molding press for applying pressure to plasticdental investment casting material, at least two elongated tubular shellmembers screw threaded together in end to end relation, one of saidshell members having a cylindrical bore formed axially therein, a pairof opposed pistons within said bore, hydraulic fluid between saidpistons, one of said pistons being attached to a hydraulic pressureapplying plunger, which plunger is apertured longitudinally and carriesa pressure gauge thereon which is in communication with said cylindricalbore through said aperture in said plunger, said second piston beingattached to a fluid responsive plunger fitted in the other end of saidcylindrical bore, which plunger extends outwardly therefrom, meansretaining said plunger within said cylinder, a spring interposed betweensaid cylinder and said plunger to urge said plunger into said cylinder,said second mentioned elongated, tubular shell memberhaving an abutmentintermediate the length thereof, which abutment is centrally apertured,said outwardly extending end portion of said fluid responsive plungerbeing adapted to extend through said apertured abutment into said lastmentioned tubular shell member, said last named tubular shell memberbeing adapted to receive a molding flask having an axial hole formedtherein, and screw means in said second mentioned tubular member at theend remote from said cylindrical bore, for retaining said molding flaskwithin said tubular member.

References Cited in the file of this patent UNITED STATES PATENTS

